Merge pull request #21329 from poettering/homed-compress-default

homed: default to btrfs compression

docs/ENVIRONMENT.md

@@ -433,3 +433,9 @@ SYSTEMD_HOME_DEBUG_SUFFIX=foo \
       SYSTEMD_HOME_RECORD_DIR=/var/lib/systemd/home.foo/ \
       /home/lennart/projects/systemd/build/systemd-homed
 ```
+
+* `$SYSTEMD_HOME_MOUNT_OPTIONS_BTRFS`, `$SYSTEMD_HOME_MOUNT_OPTIONS_EXT4`,
+  `$SYSTEMD_HOME_MOUNT_OPTIONS_XFS` – configure the default mount options to
+  use for LUKS home directories, overriding the built-in default mount
+  options. There's one variable for each of the supported file systems for the
+  LUKS home directory backend.

src/home/homework-mount.c

@@ -20,12 +20,23 @@
 #include "user-util.h"
 
 static const char *mount_options_for_fstype(const char *fstype) {
+        const char *e;
+        char *n;
+
+        assert(fstype);
+
+        /* Allow overriding our built-in defaults with an environment variable */
+        n = strjoina("SYSTEMD_HOME_MOUNT_OPTIONS_", fstype);
+        e = getenv(ascii_strupper(n));
+        if (e)
+                return e;
+
         if (streq(fstype, "ext4"))
                 return "noquota,user_xattr";
         if (streq(fstype, "xfs"))
                 return "noquota";
         if (streq(fstype, "btrfs"))
-                return "noacl";
+                return "noacl,compress=zstd:1";
         return NULL;
 }